WEEK 4 Flashcards
How do you find a short or earth, WITHOUT a current clamp?
AT RELAYS: Clip + lift = 100V = short or earth. If another clip + lift = 0V = earth, 100V = short.
AT T FUSES: Make a disconnection (remove fuses). If 100V is read = short or earth. If fuse —> earth = 100V = earth at supply. If fuse —> earth = 0V, no earth at cap.
AT TR FUSES: Make a disconnection (removed fuses). If 100V is read = short or earth, now between here and relay. Update DSIM and request wire change. If 0V is read, short or earth out on track.
When would the paralleling of a capacitor be necessary? How do we wire them up?
In the event of low capacitance in the circuit, where only 1 is being used in a box of 2, we could parallel in another capacitor. We wire the output of the current one to the output of the spare one, and the input of the current one to the input of the spare one.
What could cause low current in the circuit?
Low current could be a result of poor weather conditions causing wet beds, or a partial short or earth.
When would we parallel in a Track Transformer?
In the event of low current in the circuit, we need to increase it. However, overcurrent could overheat the transformer, as it has a maximum current limit, depending on its’ VA rating. We can therefore parallel in another transformer, to ensure current increases, but the voltage stays the same.
How do we ensure the Track Transformer is wired in parallel?
We must first add a test wire, from t0 to t0. Then, place the voltmeter from t1 to t1. If the voltmeter reads 0V, this means the transformers are in phase, so the voltmeter can be replaced with a wire.
If the voltmeter reads 200V, this would mean the transformers are out of phase, so the wire would need to be moved from t1 to t1, to t1 to t2.
What are the 2 methods of Paralleling a Track Transformer?
- Track transformer to spare track transformer.
- Track transformer to spare 7-way position.
What is the method for paralleling in a track transformer to a spare track transformer?
- Test meter and get AWC. Isolate the floating track.
- Connect a wire from t0 —> t0. Insert the fuses for both.
- Place voltmeter from t1 —> t1. If it reads 0V, this means it is in parallel, in phase. Replace voltmeter leads with wire. If it reads 200V, this means it is in series, out of phase. Move the wire from t0 —> t1, and recheck voltmeter.
What is the method for paralleling in a track transformer to a spare 7-way position?
1.Test meter and get AWC. Isolate the floating track.
- Wire to isolating transformer first, to remove the Earth supply.
- Connect a wire from t0 —> t0. Insert the fuses for both.
- Place voltmeter from t1 —> t1. If it reads 0V, this means it is in parallel, in phase. Replace voltmeter leads with wire. If it reads 200V, this means it is in series, out of phase. Move the wire from t0 —> t1, and recheck voltmeter.
What are the 2 purposes of position detectors?
- Route exit device - If they were too close to points, we could release locking too soon. If they were too far, it would slow the movement of trains and be unnecessary.
- Speed control - if they were not installed in the same position, it will not accurately detect speed control.
What do we have around tight bends?
- Speed limit and speed control.
- Check rails
- Repeaters
How do we find an earth or short in a Trainstop Proving TQ circuit?
If we have an earth or short, the fuse will blow. The TR will be down and the trainstop will be ‘ON’.
- Q1-Q2 = 0V.
- Missing potential test: Q1 - earth = 0V = missing BX.
- 1F - earth = 0V = fuse is blown.
- As soon as we put another fuse in, it will blow.
DECIDE IF IT’S A SHORT OR EARTH:
- Remove NX from busbar and replace fuse. If fuse blows = earth. If fuse holds = short.
- Get an AWC, replace NX, and make disconnections to locate fault, replacing fuse each time.
Why do we have wire degradation checks?
Degradation raises the risk of false-feeding vital signalling circuits.
What are the different types of wire degradation?
- Green spots
- Liquefaction
- Shrinkage
- Red spots
- Twigletts
- Embrittlement
- False alarms
What is the most dangerous type of wire degradation?
Green spots are the most dangerous as they have electrical conductivity so can cause electric shocks, and because of the speed at which it can develop. We must also check for neoprene based insulation and PVC cable ties, as this can accelerate wire degradation.
What should you do if you come across wire degradation?
- Take a picture to send to DSIM.
- DO NOT TOUCH!
- It should be reported and then sleeved as soon as possible.
What could be a possible outcome of wire degradation?
It could false feed equipment and cause wrong-side failures.
If liquid was leaking from a capacitor or transformer, what could it be?
The liquid in question are low viscosity clear oils. The oil often contains a proportion of PCB, which can build up in the body and cause illness.
What are the measurements for a trainstop?
- 3 ‘’ +/- 1/8
- 6’’ +/- 1/16
- minimum 5 1/2’’
What are the requirements when gauging a tripcock tester?
- The light comes on when a train is on the track.
- If it’s too tight, low, or wide, it will hit the gate and trip the train.
- If it’s too high, it won’t trip the train and the light will stay on.
What are the requirements when gauging a position detector?
- It must be 41 from top of rail, +/- 1mm, and placed back in the exact same position after a re-rail.
- Put dummy wheel on P.D.
- Check the evaluator card to check that the light has gone off.
- When removed, observe it come back on.
- For a delta, the same process applies but with a shunt on track, then the relay must be checked.
What are the fundamental principles of signalling?
- Safe passage of trains over points and crossings.
- Safe distance between trains.
Which engineering standard provides guidance on track circuit maintenance?
S2541
Which engineering standard provides guidance on irregular connections / adjustments?
S2530
